1. Field of the Invention
The present invention relates to a technical field concerning display devices (hereinafter referred to as light-emitting devices) comprising, on a substrate, an element (hereinafter referred to as a light-emitting element) having a structure comprising an anode, a cathode, and a thin film (hereinafter referred to as a light-emitting layer) sandwiched between the anode and the cathode to emit light relying upon a phenomenon called electroluminescence. The invention further relates to a technical field concerning an electronic device provided with the light-emitting device as an video display portion.
2. Description of the Related Art
In recent years, it has been urged to develop a light-emitting device referred to as an organic EL panel, an organic light-emitting diode (OLED) and the like as video displays. This is realized by generating a light-emitting phenomenon called electroluminescence by recombining holes and electrons in the light-emitting layer formed between an electrode (hereinafter referred to as an anode) for injecting holes and an electrode (hereinafter referred to as a cathode) for injecting electrons, and by controlling on/off of light emission to display images.
A thin organic film is mainly used as a light emitting layer used for the light-emitting device. An evaporation method had been a favored method for forming the thin organic film by using a low molecular weight material. At present further, however, a method has been vigorously developed for forming the light-emitting layer comprising a high molecular weight material used for the light-emitting device by applying a solution, such as by a spin-coating method, an ink jet method or a printing method. In particular, formation of a thin organic film by the ink jet method is already approaching a practicable level, and its basic technology has been disclosed in, for example, JP10-012377.
The ink jet method is technology accomplished by applying the ink jet method that has heretofore been used in the printers to the formation of thin films, by using, instead of an ink, a solvent such as water or an alcohol in which is dissolved or dispersed a solute that is a material of the organic thin film, and applying a droplet solution to each of the pixels. As a matter of course, since a droplet solution attached onto pixels (which are pixel electrodes provided in the respective pixels, in fact) includes a lot of solvent ingredients, an additional step for vaporizing the solvent ingredients (hereinafter referred to as a step for firing) is required in order to remove the solvent ingredients. That is, after the droplet solution is applied by the ink jet method, each of the pixels is heated entirely to vaporize the solvent ingredients, thereby reducing the thickness of remaining solute (which is a material for an organic thin film).
Such step for firing is generally conducted in an electric heating furnace, therefore it causes a reduction of throughput. Further, it is hard to vaporize the solvent ingredients at low temperature, and when the solvent ingredients are remained in a thin film, the ingredients are vaporized with time to cause a degassing phenomenon, thereby causing deterioration of the organic thin film. Furthermore, deterioration of a light emitting element is caused. In addition, when heating temperature is increased in order to remove the solvent ingredients completely, the composition of the organic thin film that has low heat resistance is destroyed.
As set forth above, although the film formation method using the ink jet method has the advantage of being able to manufacturing a light emitting device at low cost, through a simple method and featuring a high throughput, the film formation method is a technique that leaves to be improved at a point in which the step for firing is necessary.